Blenheim Stalk is a well-known expert on Muggles and the author of several books, including Muggles Who Notice (FB, FW).
Writing; (presumably) researching Muggles
"Blenheim" may refer to Blenheim Palace and/or the Oxfordshire civil parish in which the palace is located. Blenheim Palace has been the home of the Churchill family since its construction in the early 1700s, and it is probably best know today as the birthplace of Winston Churchill (source: Wikipedia). The EA wizard card picture of Blenheim Stalk arguably looks like a mustachioed Winston Churchill.
"Stalk" probably hints at the way he has to conduct his research.